Four measurements and four minutes to settle it!

It's the difference between the right size arriving and the wrong one.

(Please use the dimension drawing below as an aid)

Here are the PDF Drawings for the required measurements and general clearance information.

If anything is still unclear, feel free to contact me.

Find your tank below, then measure yours to confirm. The spans come from manufacturers' published dimensions, not my measurements, so they're a good starting point, not a guarantee.

Send me your measurements, and I'll tell you which one fits.

On the biggest tanks both will fit. The question is how much of the tank gets swept.

On a tank around 610 mm front to back, the 430's carriage travels across about 70% of the span and the 470's about 77%. The rest, at each end, is where the drive and electronics sit. It isn't wasted space, but it isn't sweep either.

Under 600 mm front to back — the 430. The 470 won't fit.

640 mm or more — the 470, with room to spare.

Between the two — either works. The 430 saves you £60; the 470 travels 40 mm further.

If you're on the fence, take the 430. It's the more forgiving fit, and 40 mm of extra travel is not what makes this work — moving the origin at all is.

The housing prints in two halves. Longer would mean three, which puts a second joint into the part carrying the linear rail — and I'd rather have a shorter sweep than a less rigid one. That's where 470 comes from.

A eurobrace is a glass ledge bonded inside the top edge to stop the panes bowing. Whether it gets in the way here comes down to one question: does it run along the back?

The unit clamps to the rear rim, so it needs the inside face of the back glass clear. If the back is braced, the standard clamp can't reach past it. If the back is open — which some makers do, bracing the front and the two sides only — the rear clamp lands normally, and what's left is the front support, which has a ledge of glass where it expects an open rim.

A eurobrace clamp variant is in development. Before you order, measure your brace — how wide it is, and whether it runs along the back — and message me. I'll tell you where it stands for your tank.

Red Sea REEFER G3, 425 and above.

Braced along the front and the two sides, about 79 mm wide, with the back pane bare. So the rear clamp is fine on these, and it's only the front support waiting on the variant.

The unit clamps to the rear rim at one end of the tank and sweeps front to back, so a weir only matters if it is in that end.

Central weir — no problem. That is the common layout on reef-ready tanks, and the unit sits to one side of it. You can run one at each end.

Corner or end weir. It occupies exactly where a unit wants to go. Put the unit at the other end. If you were planning two, one end is out unless there is clear rim outboard of the weir — worth measuring and letting me know before you order.

Full-width rear overflow. This works — you just measure differently. The clamp lands on the weir wall rather than on the back glass, so the drive end sits over the weir instead of behind the tank. Check the weir is at least 65 mm front to back, and in return you need no clearance at all behind the cabinet. The sweep itself stays entirely over the display.

What changes is the number you order from: measure front glass to the weir wall, not the full depth of the tank. On a shallow display that can put you a size down, or below the smallest unit — so that measurement comes first.

One measuring note that covers all three: the figure that picks your model is the display area, front to back, at the end where the unit will actually sit. Not the outside of the tank, and not down the middle.

Red Sea ask for at least 100 mm behind a REEFER — for cable access and airflow, not for the tank — and most makers don't publish a figure at all. In practice people leave more than 100 mm, because that's what it takes to get an arm and a tool back there. So the 65 mm the standard mount needs is already there on the great majority of tanks.

This section is for the ones where it isn't: an alcove, a peninsula pushed against a wall, or a tank that went in tighter than the manual asked for.

I'm developing a kit that moves the primary clamp off the back rim and onto the side glass. The front support already sits there, so both ends would hold the same pane — and because a clamp on the side rim can sit anywhere along it, you choose how far back the unit goes instead of the back glass deciding for you. Pushed fully back the drive end overhangs by around 30 mm, less once your glass thickness comes off it. Bring it forward a couple of centimetres and it sits flush, with nothing behind the tank at all.

The trade is where the sweep lands. Move the unit forward and the whole travel comes forward with it, so you buy clearance at the back and give up a little reach behind the rockwork. That's a judgement about your own aquascape rather than a number I can put in a table, which is why choosing a size for this kit is a conversation rather than a lookup.

It isn't finished and those figures are targets, not final. If your tank is tight behind, message me with the gap you've actually got and I'll tell you where the kit has got to.

Please review our How it works page for all the details.

Please review our Compatible Pumps page for all the details.